Audio Equalizer Circuits
An equalizer can be used to correct or flatten the frequency response of speakers rather than designing the speaker itself to be equalized. In a graphic equalizer circuit, the input signal is sent to a bank of filters. Each filter passes the portion of the signal present in its own frequency range or band. The amplitude passed by each filter is adjusted using a slide control to boost or cut frequency components passed by that filter.
On the other hand Parametric equalizer circuits are multi-band variable equalizers which allow users to control the three primary parameters: amplitude, center frequency and bandwidth. The amplitude of each band can be controlled, and the center frequency can be shifted, and bandwidth can be widened or narrowed. Equalizers can correct problems posed by a room's acoustics, as an auditorium will generally have an uneven frequency response especially due to standing waves and acoustic dampening.
A variant of the parametric equalizer is the semi-parametric equalizer circuits, also known as a sweepable filters. Allows users to control the amplitude and frequency, but uses a pre-set bandwidth of the center frequency. In some cases, semi-parametric equalizers allow the user to select between a wide and a narrow preset bandwidth.